Ignition systems

ABSTRACT

A capacitive discharge ignition system which does not use transistors and which transfers power from the vehicle battery to the discharge capacitor both inductively and capacitively thereby resulting in increased efficiency. The primary winding of a stepup transformer is connected in series with the vehicle battery and the distributor points and transfers energy to a discharge capacitor connected in the secondary circuit of the transformer when the points close. The discharge capacitor is also charged by energy from another capacitor in the secondary circuit which is charged during the previous points open period. The discharge capacitor is connected in parallel with the series combination of an SCR and the ignition coil of the vehicle and discharges through the ignition coil to provide spark energy when the SCR is turned on by the points opening. Reverse biasing of the gateemitter junction of the SCR begins shortly after turn on to prevent misfire and to facilitate turn off of SCR when the anode of the SCR becomes back-biased.

United States Patent 1 Mackie v 111 3,300,771 1 Apr. 2, 1974 1 IGNITIONSYSTEMS [76] Inventor: Ronald D. Mackie, Rt. 1, Box 776-P,

Pensacola, Fla. 32507 221 Filed: Mar. 10, 1972 y 21 Appl. No.: 233,623

Related US. Application Data [63] Continuation of Ser. No. 80326, Oct.15, 1970,

Primary ExaminerLaurence M. Goodridge Assistant ExaminerRonald B. Cox

Attorney, Agent, or Firm-Browne, Beveridge, Degrandi & Kline [57]ABSTRAT A capacitive discharge ignition system which does not usetransistors and which transfers power from the vehicle battery to thedischarge capacitor both inductively and capacitively thereby resultingin increased efficiency. The primary winding of a step-up transformer isconnected in series with the vehicle battery and the distributor pointsand transfers energy to a discharge capacitor connected in the secondarycircuit of the transformer when the points close. The dischargecapacitor is also charged by energy from another capacitor in thesecondary circuit which is charged during the previous points openperiod. The discharge capacitor is connected in parallel with the seriescombination of an SCR and the ignition coil of Y the vehicle anddischarges through the ignition coil to Claims, 1 DQ111515???" CR-G Thisapplication is a continuation of U. S. Pat. application Ser. No. 80,326filed in the same of Ronald D. Mackie on Oct. 15, 1970, now abandoned.

The invention relates to an improved capacitive discharge ignitionsystem for an automotive vehicle. While such discharge systems are knownin the prior art, they are usually complicated electronic circuitsincluding one or more switching transistors used to supply the dischargecapacitor with energy from the battery of the vehicle. For instance, itis common in prior art discharge systems to utilize transistorizedmultivibrator or inverter circuits to supply the discharge capacitorwith energy. Such circuits besides containing a number of components andtherefore adding to the cost of the system, consume power, and thereforedo not provide for the most efficient transmission of the energy of thevehicle battery to the discharge capacitor. Additionally, thetransistors are heat-sensitive and require heat sinksto' effectivelyoperate in the heated environment of the automotive engine.

7 The present invention eliminates the transistorized multivibrator orinverter circuitry by using the opening and closing of the distributorpoints to directly transfer energy to the discharge capacitor through astep-up transformer. Additionally, a second capacitor is charged duringa portion of the cycle and adds to the energy transferred to thedischarge capacitor by the 'step-up transformer thereby increasing theefficiency of power'transfer from the vehicle battery to the dischargecapacitor. Further, a novel circuit is provided which results inimproved biasing and triggering of the SCR.

lt is therefore an object of the invention to provide a capacitivedischarge ignition system which contains a minimum of parts, is simpleand inexpensive to fabricate, and provides improved performance for longperiods of use. 1

It is a further object of the invention to provide a catively therebyincreasing the efficiency of the system.

It is a further object of the invention to provide an improved method oftriggering the SCR and of backbiasing the gate-emitter junction of theSCR when it is not being triggered.

It is a further object of the invention to provide an improved circuitin which voltage fluctuations at the anode of the SCR are reduced toprevent misfire of the SCR.

lt is a further object of the invention to provide direct chassisgrounding of the SCR anode which results in simpler and cheaper mountingof the SCR, better transfer of heat from the SCR, and elimination of thepossibility of a short occurring between an anode insulated from thechassis and the chassis.

It is a further object of the invention to provide for improvedself-cleaning action of the distributor points.

It is a further object of the invention to provide a capacitivedischarge ignition system which will work equally well with positiveground or negative ground engines.

The above objects are accomplished by providing a capacitive dischargeignition system in which the energy of the vehicle battery is directlytransferred to the discharge capacitor by the opening and closing of thedistributor points. The primary winding of a step-up transformer isconnected in series with. the points and the vehicle battery, and thesecondary winding of the transformer is connected to a circuit includingthe discharge capacitor. The discharge capacitor is charged when thepoints are closed by the energy at the secondary of the transformer andby energy stored in a capacitor in the secondary circuit during theprevious points open period. The discharge capacitor is connected inparallel with the series combination of an SCR and the primary of theignition coil and when the points open the gate-emitter junction of theSCR becomes forward biased to turn the SCR on thereby providing acurrent path for the charge stored on the discharge capacitor throughthe SCR and the ignition coil. Shortly after turn on the gate-emitterjunction of the SCR becomes back biased by a novel circuit thus insuringthat the SCR willbe turned ofi 'when the anode is back biased. Thecurrent energy which is not consumed by the spark or by the resistanceof the ignition coil transfers back to the discharge capacitor withinthe opposite direction and when it reaches the maximum of the directionof current, reverses through the ignition coil thereby forward biasing adiode connected across the anode emitter junction of the SCR and reversebiasing the anode which in conjunction with the reverse bias of theemitter gate junction turns the SCR off until the points open again.

The invention will be better understood by referring to the FIGURE inconnection with the following detailed description of a preferredembodiment of the invention.

Referring to the FIGURE, T1 is a standard step-up transformer, thesecondary of which, in the preferred embodiment of the invention, iseither center-tapped or wound in separate halves which are connectedtogether at the center. T1 is wound so that if one end of the completesecondary is negative relative to the center tap the other end of thecomplete secondary will be positive relative to the center tap. 1n thepreferred embodiment of the invention, a step-up ratio of 1:32 is usedfor the complete secondary embodiment. While a center tap secondary forT1 and a turns ratio of 1:32 are used in the preferred embodiment of theinvention, it should be noted that other tap locations and turn ratioscan be used to obtain the operating characteristics which will bedescribed hereafter.

The primary winding of T1 is connected in series with the standardvehicle battery, the ignition switch, the standard ballast resistor,which may be approximately 3 ohms, and the distributor points. Thecapacitor connected across the distributor points is the standard pointscapacitor. The connections from the ballast resistor and the points tothe primary winding of T1 should be made so that the end of thesecondary winding of T1 connected to CR-l will be negative going withrespect to the opposite end of the secondary when the current throughthe primary of T1 is interrupted by the points opening. As noted above,the present invention can be used with either a negative ground engineor a positive ground engine and assuming that the primary of T1 is woundso that the Pl terminal is negative going with respect to the P2terminal when the current through the primary is interrupted by thepoints opening, in a negative ground engine the wire from the pointsshould be attached to the P2 terminal and the wire from the ballastresistor should be attached to the Pl terminal while in a positiveground engine the connections should be reversed. In this way witheither a negative or positive ground engine, current will flow throughthe primary of T1 in the same direction when the points are closed.

The primary winding of the ignition coil is also connected in adirection dependent on whether the engine is positively or negativelygrounded. Proper connection to the ignition coil will insure that thespark voltage applied to the insulated electrode of the spark plug willbe negative with respect to engine ground. In a negative groundinstallation the terminal P3 is connected to the minus terminal of thespark coil and P4 is connected to the plus terminal, while in a positiveground engine the connections are reversed.

The ignition coil is connected in series with the SCR and the seriescombination of the ignition coil and the SCR is connected in parallelwith capacitor C1 which is the discharge capacitor of the invention. Asin all capacitive-discharge ignition systems, a charge stored ona-discharge capacitor will discharge through a switch which is turned onperiodically to supply a high voltage of short rise time duration to theignition coil for firing a spark plug. In the present invention the SCRis the switch and the charge accumulated on discharge capacitor Cldischarges through the ignition coil when the SCR is triggered on by aforward bias signal applied to its gate-emitter junction.

It should be noted that the anode of the SCR is directly connected toground. This connection permits direct and simplified mounting of theSCR to a metal ignition system enclosure which is directly connected toengine ground or chassis ground permitting more efficient heat transferaway from the anode and eliminating the chance that an insulated SCRanode has of shorting to the chassis or engine ground.

One of the features of the present invention is that energy from thevehicle battery is supplied to capacitor C1 not only through theinductive means of the transformer but also through capacitor C-2. C-2in combination with the lower half of the T1 secondary and diodes CR-3and CR-4, resistor R-l, capacitor C-3 and the emitter-gate junction ofthe SCR form a resonant circuit for transmitting inductive energy storedin the transformer T-l to capacitor C-2 as voltage energy.

The operation of the invention will now be described. As indicatedabove, transformer T-l is connected and wound so that when the pointsopen, the end of the secondary winding connected to CR-l will benegative going with respect to the opposite end of the secondary. Whenthe points are opened, therefore, one of the things which happens isthat current travels from the bottom half of the secondary winding tocapacitor C-2 thereby charging capacitor C-2. The size of capacitor C-2is chosen with respect to the engine RPMs and the other components inthe circuit so that it is fully charged and has already begun todischarge by the time that the points close. When the points closetherefore C-2 will be somewhere in the process of transferring energy todischarge capacitor C4 through the entire secondary winding oftransformer T-l.

Due to the step-up ratio of transformer T1, as the points close ahighvoltage is placed in series aiding with discharging capacitor C2across discharge capacitor C-l. If a 1:32 step-up ratio and a 3-ohmballast resistor are used, then an apparent voltage source ofapproximately 384 volts having an internal resistance of approximately3072 ohms will be effectively placed in series with capacitor C2when'the points close. Then capacitor C-l is charged to a maximumvoltage from the energy in the secondary of the transformer combinedwith the energy transferred to capacitor C2 during the previous pointsopen period. After most, if not all, of the stored energy on capacitorC-2 has been used to charge capacitor C1, diode CR-2 which is connectedacross capacitor C-2, prevents any remaining charging current throughC-l from reverse charging C-2.

After discharge capacitor C-l is charged to its maximum voltage, thepoints open'and O2 is charged as described above.

The charging of capacitor C-2 through resistor R-l causes current toflow through R4 in the forward bias direction of diode CR4 and causes avoltage across resistor R-l which is effective to forward bias thegateemitter junction of the SCR thereby turning the SCR on a short timeafter the points open. Diode CR-4 equalizes the variable resistanceemitter-gate junction of the SCR and insures that there will be adequatecurrent flow through the emitter-gate junction as the points open topositively fire the SCR. The turned-on SCR is an effective closed switchand along with the ignition coil forms a low resistance path acrossdischarge capacitor C-l. The stored charge on capacitor C-l immediatelydischarges through the ignition coil in a direction from terminal P-3 toterminal P-4 and through the SCR. Due to the extremely rapid rise ofvoltage across the primary of the ignition coil the time during whichthe voltage rises to the sparking potential of the spark plug isextremely short and herein lies the great advantage of the capacitordischarge ignition system over the conventional points ballast ignitionsystem. The extremely short rise time in which the large voltage of C-1is impressed across the primary of the spark coil can mean thedifference between firing and not firing the spark plug.

After tum-on the SCR cannot be turned off merely by reverse biasing thegate-emitter junction but rather both the gate-emitter junction and theanode must be back biased to efiect turn off. One of the novel featuresof the invention is the provision of means which begins to back bias.the gate-emitter junction of the SCR immediately following turn-on soas to prevent misfire and so that the SCR can be turned off as soon asthe anode is back biased and this means will now be described.

When the points open and as the current increases through resistor R-lto forward bias the gate-emitter junction of the SCR, capacitor C-3 ischarged. The current increases through resistor R-l to the point whereit equals the charging current through the capacitor C-2. After thispoint the current begins to decrease through resistor R-l untilcapacitor C-2 reaches full charge and when capacitor C-2 does reach fullcharge the voltage across resistor R-l will be zero. While the currentthrough resistor R-l is decreasing, capacitor C-3 discharges throughdiode CR-S, thereby backbiasing the SCR. When capacitor C2 completescharging as described above, it begins to transfer energy to capacitorC-l through the secondary of the transformer and through diode CR-Sthereby maintaining the back biasing of the gate-emitter junction untilthe points close again when back biasing is continued until either thecompletion of the charging of capacitor C-l or until the points openwhich might occur before the completion of charging of capacitor C-l athigher engine speeds. Thus it is seen that according to the novelcircuit arrangement of the invention, the back biasing of the SCR beginsto take place shortly after turn-on and continues right through untilthe charging of capacitor C-l is completed or until the points openagain.

After the SCR is turned on, current builds up to a peak in the primaryof the spark coil about the time that the voltage on discharge capacitorC-l has dropped to zero. Whatever current energy is not consumed eitherby the spark itself or by the resistance of the spark coil windingsbegins to transfer back to capacitor C-l as voltage energy which isopposite in polarity to the voltage energy which was originally storedon capacitor C-l from the battery. When the voltage on capacitor C-lreaches a maximum in the opposite direction current reverses through theprimary of the spark coil forward biasing and flowing through diode CR-6and thereby reverse biasing the anode of the SCR which in conjunctionwith the reverse biasing of the gate-emitter junction previouslydescribed turns the SCR off until the next opening of the points.

Current flow continues through diode CR-6 until most of the currentenergy remaining in the spark coil is returned to capacitor C-l withthesame voltage polarity as the voltage energy which will be added tocapacitor C-l from the battery. This energy returned to C-1 from thespark coil combines with the energy added to C-1 from the battery whenthe points close again and from capacitor C-2. The energy in the sparkcoil not returned to capacitor C-l oscillates until damped bycoilresistance. These oscillations which cause voltage fluctuations at theanode of the SCR are normally too weak by themselves to cause SCRmisfire and are allowed to die out before being added to the voltagefluctuations caused by the charging of capacitor G1 with energy from thebattery.'The fact that energy not used in firing a spark plug isrestored to C-1' for release the next time the points open allows thepractice of bypassing the ballast resistor to be dispensed with.

One of the novel features of the invention is the connection of thedischarge capacitor in parallel with the series combination of theignition coil and the SCR. This location of discharge capacitor C1prevents charging currents to 01 via CR-l from passing through theprimary of the spark coil which if allowed to happen could cause voltagefluctuations at the anode of the SCR sufficient to cause misflre.

Another advantage of the invention is that the circuit provides forself-cleaning of the distributor points by allowing adequate current toflow through the points while simultaneously reducing the inductiveeffect which tends to cause arcing in a conventional ignition system.This inductive efiect is reduced by the reflection of a substantialcapacitance in parallel with the primary of the transformer each timethe points open. The tendency of the primary inductance of thetransformer to hold an arc across the points is reduced to the extentthat the invention can operate with the standard points capacitorcompletely removed.

Typical values for the components of the invention are listed below:

T-l 4 M.h. primary 4 a. D C, 1:32 turns ratio C-1 1 MFd, 600vDC G2 0.25MFd 1000vDC C-3 0.01 MFd 200vDC R-l 47 ohms, 1 watt The above values areillustrative only and should not be construed to be limiting. They havebeen found to work satisfactorily at typical engine speeds, up to thosespeeds at which a complete cycle from points opening to points openingwould be about 2000 microseconds. The SCR can be a General Electric typeGEX-l6 or equivalent and all diodes are standard semiconductive diodessuch as silicon diodes. The capacitor C-2 is sized to provide adequatetrigger current for the SCR, to provide for rapid transfer of energyfrom the primary winding of T-l to C-2 and to insure that most, if notall, of the energy stored on O2 is transferred to G1.

There has thus been described above a capacitive discharge ignitionsystem which does not use transistors and which operates efficiently.

While I have disclosed and described the preferred embodiment of myinvention, I wish it understood that I do not intend to be restrictedsolely thereto, but that I do intend to include all embodiments thereofwhich would be apparent to one skilled in the art and which come withinthe spirit and scope of my invention.

1 claim:

l. A capacitive discharge ignition system which transfers energy fromthe battery of a vehicle to a discharge capacitor without the use ofswitching transistors, comprising: 1

a step-up transformer having a primary winding and a secondary winding,said primary winding being connected in series with said vehicle batteryand the distributor points of said vehicle, a discharge capacitor, asilicon controlled rectifier and an ignition coil being connected incircuit relationship with each other and with the secondary winding ofsaid transformer, means for applying the voltage across said secondarywinding of said transformer. to said discharge capacitor when saidpoints close to charge said discharge capacitor without the use ofswitching transistors, means for discharging said discharge capacitorthrough said silicon controlled rectifier and said ignition coil whensaid points open to provide an ignition spark, and means for aiding saidtransformer in charging said discharge capacitor, said means for aidingincluding a storage capacitor and means for charging said storagecapacitor when said points open.

2. The system of claim 1 wherein said discharge capacitor is connectedin parallel with the series combination of said silicon controlledrectifer and said ignicapacitor to discharge through said siliconcontrolled rectifier and said ignition coil.

4. The system of claim 3 further comprising means for back-biasing saidgate-emitter junction of said silicon controlled rectifier shortly afterturn-on so that said silicon controlled rectifier will be turned offwhen its anode becomes back biased.

5. The system of claim 4 wherein said means for triggering saidgate-emitter junction of said silicon controlled rectifier includes aresistor connected in the secondary circuit of said transformer and thegate-emitter circuit of said silicon controlled rectifier, said resistorbeing supplied with current when said points open to impress a forwardbias voltage across said gate-emitter junction.

6. The system of claim 5 wherein said means for back-biasing comprisesthe series combination of a capacitor and diode connected in saidgate-emitter circuit and in parallel with said resistor, said capacitorbeing charged by the current flowing through said resistor, and beingdischarged through said diode to back bias said gate-emitter junction.

7. The system of claim 6 further comprising a diode connected across theanode-emitter junction of said silicon controlled rectifier in adirection opposite to the direction of the anode-emitter junction forturning said silicon controlled rectifier off.

8. The system of claim 6 wherein the anode of said silicon controlledrectifier is directly connected to ground.

9. The system of claim 8 wherein a capacitance proportional to thecapacitance of said storage capacitor is effectively placed in parallelwith said primary winding of said transformer each time said points openthereby compensating for the inductive effect of the primary winding ofsaid transformer and permitting said points to be cleaned by currentpassing through them.

10. A capacitive discharge system for connection in a secondary winding,said primary winding being adapted for series connection with saidvehicle battery and said distributor points, a discharge capacitor and asilicon controlled rectifier in circuit connection with each other andwith the secondary winding of said transformer, means for charging saiddischarge capacitor from the secondary winding of said transformer whencurrent increases through said primary winding of said transformer andmeans for discharging said discharge capacitor through said siliconcontrolled rectifier when current decreases through said primary windingof said transformer, a storage capacitor connected in series with thesecondary winding of said transformer, means for charging said storagecapacitor when the current in the primary winding of said transformerdecreases and means for discharging said storage capacitor to aid incharging said capacitor, whereby when said primary winding is connectedin series with said vehicle battery and said points, and said ignitioncoil is connected in series with said silicon controlled rectifier, saiddischarge capacitor is charged when said points close and is dischargedthrough said ignition coil to provide an ignition spark when said pointsopen.

11. The system of Claim 10 wherein said discharge capacitor is connectedin parallel with said silicon controlled rectifier and said means fordischarging said discharge capacitor comprises means for triggering thegate-emitter junction of said silicon controlled rectifier with aforward bias signal to turn said silicon controlled rectifier on,whereby when said ignition coil of said vehicle is connected in serieswith said silicon controlled rectifier said discharge capacitor willdischarge through said ignition coil, means for back biasing the gateemitter junction of said silicon controlled rectifier shortly afterturn-on so that said silicon controlled rectifier will be turned offwhen its anode becomes back biased, said means for back-biasing thegate-emitter junction comprising the series combination of a capacitorand a diode connected in the gate-emitter circuit.

1. A capacitive discharge ignition system which transfers energy fromthe battery of a vehicle to a discharge capacitor without the use ofswitching transistors, comprising: a step-up transformer having aprimary winding and a secondary winding, said primary winding beingconnected in series with said vehicle battery and the distributor pointsof said vehicle, a discharge capacitor, a silicon controlled rectifierand an ignition coil being connected in circuit relationship with eachother and with the secondary winding of said transformer, means forapplying the voltage across said secondary winding of said transformerto said discharge capacitor when said points close to charge saiddischarge capacitor without the use of switching transistors, means fordischarging said discharge capacitor through said silicon controlledrectifier and said ignition coil when said points open to provide anignition spark, and means for aiding said transformer in charging saiddischarge capacitor, said means for aiding including a storage capacitorand means for charging said storage capacitor when said points open. 2.The system of claim 1 wherein said discharge capacitor is connected inparallel with the series combination of said silicon controlled rectiferand said ignition coil.
 3. The system of claim 2 wherein said means fordischarging said discharge capacitor comprises means for triggering thegate-emitter junction of said silicon controlled rectifier with aforward bias signal to turn said silicon controlled rectifier on andcause said discharge capacitor to discharge through said siliconcontrolled rectifier and said ignition coil.
 4. The system of claim 3further comprising means for back-biasing said gate-emitter junction ofsaid silicon controlled rectifier shortly after turn-on so that saidsilicon controlled rectifier will be turned off when its anode becomesback biased.
 5. The system of claim 4 wherein said means for triggeringsaid gate-emitter junction of said silicon controlled rectifier includesa resistor connected in the secondary circuit of said transformer andthe gate-emitter circuit of said silicon controlled rectifier, saidresistor being supplied with current when said points open to impress aforward bias voltage across said gate-emitter junction.
 6. The system ofclaim 5 wherein said means for back-biasing comprises the seriescombination of a capacitor and diode connected in said gate-emittercircuit and in parallel with said resistor, said capacitor being chargedby the current flowing through said resistor, and being dischargedthrough said diode to back bias said gate-emitter junction.
 7. Thesystem of claim 6 further comprising a diode connected across theanode-emitter junction of said silicon controlled rectifier in adirection opposite to the direction of the anode-emitter junction forturning said silicon controlled rectifier off.
 8. The system of claim 6wherein the anode of said silicon controlled rectifier is directlyconnected to ground.
 9. The system of claim 8 wherein a capacitanceproportional to the capacitance of said storage capacitor is effectivelyplaced in parallel with said primary winding of said transformer eachtime said points Open thereby compensating for the inductive effect ofthe primary winding of said transformer and permitting said points to becleaned by current passing through them.
 10. A capacitive dischargesystem for connection in a vehicle having a battery, a distributor withpoints and an ignition coil, comprising: a step-up transformer having aprimary winding and a secondary winding, said primary winding beingadapted for series connection with said vehicle battery and saiddistributor points, a discharge capacitor and a silicon controlledrectifier in circuit connection with each other and with the secondarywinding of said transformer, means for charging said discharge capacitorfrom the secondary winding of said transformer when current increasesthrough said primary winding of said transformer and means fordischarging said discharge capacitor through said silicon controlledrectifier when current decreases through said primary winding of saidtransformer, a storage capacitor connected in series with the secondarywinding of said transformer, means for charging said storage capacitorwhen the current in the primary winding of said transformer decreasesand means for discharging said storage capacitor to aid in charging saidcapacitor, whereby when said primary winding is connected in series withsaid vehicle battery and said points, and said ignition coil isconnected in series with said silicon controlled rectifier, saiddischarge capacitor is charged when said points close and is dischargedthrough said ignition coil to provide an ignition spark when said pointsopen.
 11. The system of Claim 10 wherein said discharge capacitor isconnected in parallel with said silicon controlled rectifier and saidmeans for discharging said discharge capacitor comprises means fortriggering the gate-emitter junction of said silicon controlledrectifier with a forward bias signal to turn said silicon controlledrectifier on, whereby when said ignition coil of said vehicle isconnected in series with said silicon controlled rectifier saiddischarge capacitor will discharge through said ignition coil, means forback biasing the gate-emitter junction of said silicon controlledrectifier shortly after turn-on so that said silicon controlledrectifier will be turned off when its anode becomes back biased, saidmeans for back-biasing the gate-emitter junction comprising the seriescombination of a capacitor and a diode connected in the gate-emittercircuit.